VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 gas gauge trouble

Don't you want to diagnose it before taking things apart. If it were me I would ground the sender wire at the tank and see what reading I get. I would also remove the wire at the tank and take the reading again. Only after these two tests would it be obvious that the problem is in the sender.

Yes, I'm going to do that. I wish I knew if it was a 90 ohm or 30 ohm. If it reads out something different than either of those numbers I guess it needs replacing. Thanks for the advice. It could be a frayed wire bewteen the sending unit and the gauge. I want to replace the wire anyway so with luck it may be that.

Steve, A good original '38 chev gas tank sending unit should read 30 Ohms. ( An 'empty' gas tank can be more explosive than a full one.) That's why a flooded motor won't start. Not enough air/too much liquid gas.

Thanks. I'll post photos of the results.

To clarify me comments, the readings I was talking about are on the gas gauge. With the wire disconnected, you should see a full reading and with it grounded it should read empty. Those two extremes I am quoting by memory!

Nice car. The term Master Deluxe doesn't mean a body style, more of a trim level so if you're asking a question about a door for example you need to mention it's a sedan door, not a Master Deluxe door because with a few exceptions the body panels are the same between trim levels.

Steve, if you have a multi-meter put it on ohms. Put the red lead on the wire stud and the black on the housing. Run the float full travel. It should read from ~30 ohms to ~0 on the extremes of travel with a smooth transition between. If the readings are different from that you have a sending unit problem. If the sending unit proves to be bad and you buy one of the universals drop me a note. You'll have a challenge making it work right in your tank and I can help you with that. My original sending unit was bad so I had to use a universal until I found my OEM units on ebay.

wire disconnected....gauge reads full
wire grounded to tank....gauge reads empty

Something is not working.

BTW..I see what you're talking about concerning the wire. If you lose it ,it could be a big job finding and recovering the wire. THANKS

In the morning I'm going to call the filling station to see which one of the two sending units listed they recommend, unless you already know which one to ask for. If there is any tricks to getting the aftermarket unit to work...I'm all ears.

If they actually have the replacement ,I'm going to pull the old unit out and see if it just needs corks, if it's anything else I'll order the replacement and a couple of gaskets. I don't want to pull it before getting gaskets and having something better than what I have now.

If it were me I'd pull the current sending unit for inspection and testing. It's only seven screws (if I remember right). It comes out easily. The float arm points directly toward the back of the car. You can easily make a new gasket from rubberized gasket material from any parts house. If you prefer to buy a pre-made gasket just stick the sending unit back in the hole to keep it covered until it arrives. The only way to know for sure if you have a sending unit problem is to test it and you have to pull it to do that.

Full...38 ohms
Empty....5.8 ohms


The only thing that appears to be unusual is the rivet that holds the two gears together seems to be a little sloppy, but they do mesh. The float seems okay. The unit has two "stops". Full range top to bottom is listed above. I don't think bending the float rod (toilet type adjustment) would do anything. The gears go from stop to stop.

If I understand this correctly, the stop to stop reading should be 0-30 ohms.

Any suggestions other than buy a new one?

The horizontial shaft (with spring) might be an adjustment since I'm low on one end and high on the other. Maybe?

Clean it up and reinstall. It is working okay. Never found one that went exactly to zero or just 30 ohms. Think there may be a tad of internal resistance in the connectors etc. Might tighten up the rivet if it is too loose. Lever must move smoothly.

I need a gasket...stay tuned. Thanks. I was going to try to lift the bronze clip on the horizontial shaft and turn the gear a tooth or two since it is spring loaded. I've marked the orginal postion. Better to just leave it alone? THANKS

with Chip. Your original pic shows it was pretty crusty. It's looking pretty clean now. A clean connection might make all the difference in the world. Moving it a tooth won't really do you any good I tried that on mine. It changes the full and empty readings on the gauge a bit is all. What yours is doing now should show full as above the full mark on the gauge and empty will be a bit above the empty mark. As long as you know where empty is you should be good to go.

Mission Accomplished..I think..smiles

I got it working great outside the tank and when I installed it in the tank it showed full(which it didn't before). It will take quite a while for me to burn up a full tank of gas, I'll post later if it worked on both ends of the gauge. It took 45 minutes to make a gasket that suited me...gheeez. I hate being old..smiles

THANKS to everyone for the help !! If you have a old chevy and are not a member on this forum,you've made a mistake.

lol..Takes me 45 minutes just to FIND the gasket material...So you think maybe it was just corrosion on the terminals effecting the readings...?

Steve, Before checking/removing the sending unit I would run a good wire under the car from the gauge to the sending unit to check if you have a wire problem or a sending unit problem? I would also want to make sure everything at the sending unit is well grounded. Good luck, Mike

I thought of running a "jumper wire", too. But, what the heck, they was having so much fun...lol

I think it was three things. The RIVET holding the gears together was loose, I tightened that up, next ,the connection from the wire to the sending unit was a little loose and greasy. I cleaned that up. Finally the entire unit had small pimples of rust everywhere (not sure how that could even happen). Cleaning helped alot. All I know is that at this point it's reading full like it should, if the gauge doesn't register correctly towards empty,I guess I'll tackle it again. It worked good out of the tank....who knows?

I didn't replace the wire from the gauge to the sending unit yet, another project. The wire going to the domelight also needs replacing I'm sure. The wiring was really bad when I got this ole car.

I noticed that three of the holes in the sending unit head had brass inserts of somekind, maybe that's the grounding point. I cut the gasket holes on those so they could make contact with the tank. You learn more if you do everything the hard way...smiles

Steve....That's not brass.... That is were the old guy you got the car from hid his gold...He thought that would be the last place anyone would look...Boy was he wrong...Grin..... ED.

"Seal All" comes in a small tube, flows like honey and seals anything exposed to gas or oil. I have used it to seal cork floats because they can break down in the tank. I have sealed gas tanks, pump housings.... marvelous stuff.
Mike

I'll buy some the next time I see it. Thanks for the advice. I'm always trying to repair something (maybe because I own alot of junk)...grin